1. Field of the Invention
The present invention relates to a manufacturingg method for a synthetic resin film and a device therefor, particularly to a method of treating the longitudinal side end portions (hereinafter referred to as "end portions") in the process of manufacturing a synthetic resin film and a device therefor.
2. Description of the Prior Art
A synthetic resin film such as polyimide film and polyethylene film has usually been manufactured to date by a method of first continuously extruding or applying its material, namely a fluid synthetic resin composition, in a smooth, thin film form (approximately 10-1,000 .mu.m) onto a conveyor belt or drum through a slit die or by the use of an applicator and then solidi-fying it by drying, heating or cooling.
In this manufacturing method, however, as shown in FIG. 18, for example, although the film of a fluid synthetic resin composition 2 extruded through a slit die 1 is continuously placed on a conveyor belt 3, both longitudinal end portions of the film 2 of the fluid synthetic resin are then caused to shrink by the influence of surface tension or the like and this results in formation of thick-walled portions 5, as illustrated in FIG. 19. The thick-walled portions 5 and the flat portion 6 in between of the film 2 are different in shrinkage ratio as the film 2 is solidified, the thick-walled portions 5 along both longitudinal end portions of the film 2 tend to be lifted off the surface of the conveyor belt or drum to cause shrinkage sideways to possibly interfere with manufacture of the synthetic resin film. Also, this lifting off the conveyor belt or drum surface of the film sometimes causes sideway creasing of the synthetic resin film.
For elimination of such sideway creases it was a usual practice to trim off both end portions of the synthetic resin film. The width of the strips to be trimmed off is then substantial, and the resultant decrease in yield was bound to be reflected on the film's manufacturing cost.